This invention relates to an eductor-mixer system particularly adapted for the preparation of dispersions, solutions and slurries. More particularly, the eductor-mixer system of this invention is an improvement over the eductor-mixer system disclosed in my prior U.S. Pat. No. 3,777,775.
An eductor-mixer system is well suited to continuously mix a solute (e.g., a powder, particulate, or other pressure transportable or fluidizable material, a liquid or a gas) and a solvent or working fluid (e.g., a liquid or in some instances a gas) to form a dispersion, slurry or solution. The eductor-mixer system of the present invention is especially adapted for use with readily transportable containers, such as is shown in the above-noted patent and in U.S. Pat. No. 4,007,694, in which a "semi-bulk" quantity (e.g., 500-4,000 pounds or more) of powder or other solute material is stored and transported and in which the load may be fluidized for ready discharge to the eductor-mixer system. These containers are commercially available under the registered trademark AIR PALLET from Semi-Bulk Systems, Inc. of St. Louis, Mo. The solute inlet of the above-mentioned eductor-mixer system is conventionally connected to the discharge outlet of the fluidized container so that the vacuum generated within the eductor-mixer by the flow of solvent (water) therethrough cooperates with the fluidized discharge of the powder from the container to positively draw the fluidized powder into the eductor-mixer.
In certain applications, such as in the use of fire retardants for fighting forest fires, it is often necessary to rapidly unload thousands of pounds of powdered fire retardant solute material and to mix it in proper proportion with water to form a slurry or solution for application to the fire. In many known prior art eductor-mixer systems, the powder supply, even if it were a fluidized container, was required to be located above the level of the eductor-mixer system because the latter was dependent on the gravity feed of the powder. In the system shown in the above-mentioned U.S. Pat. No. 3,777,775, the eductor-mixer system was not dependent upon gravity feed because the vacuum within the eductor-mixer positively drew the powder from the container into the eductor-mixer system and thus the system shown in the above-mentioned patent was not dependent on the relative location of the powder container and the eductor-mixer system. However, the eductor-mixer system shown in the above-mentioned patent was thought to be somewhat complex in that it utilized two stages or nozzles and it was not as efficient as was theoretically possible in generating the vacuum which positively drew the solute thereinto.
When eductor-mixers are utilized to mix abrasive powders, they are subject to destructive internal wear caused by the flow of the abrasive powder and resulting slurry within the eductor. It has been difficult to make adjustments within the eductor to compensate for wear and to accommodate different flow rates of solute and solvent through the eductor.
In many prior eductor-mixers which are used to mix a powdered solute with a liquid solvent, it has been heretofore difficult to control the flow of the powdered solute into the eductor. This was usually accomplished by a throttling valve in the solute inlet line or at the bottom of the hopper feeding the eductor-mixer with powder. This throttling valve, however, was often unsatisfactory for controlling the flow of solute in continuous operations. As shown in the coassigned U.S. Pat. No. 3,777,775, solute flow control has been achieved by providing an air bleed valve in the solute inlet line thus allowing air to enter the line and to regulate the vacuum generated within the eductor-mixer. In some instances, however, this air bleed control was not an altogether satisfactory way to control the flow of solute to the eductor-mixer.
In mixing certain solutions and solvents, it has heretofore been a problem to break up agglomerates (i.e., globules or lumps) of powder or to reduce the size of powder particles and to disperse the powder in a solvent. For example, in mixing paint pigment with a solvent, it was heretofore necessary to mechanically mix batches of the pigment and solvent in a Cowles-type blender or the like for several hours or even several days to break up and wet agglomerates of the pigment with the solvent and to uniformly disperse the pigment in the solvent.
In certain prior eductor-mixer systems, it was not possible to mix certain solute and solvent mixtures in sufficient proportion to form slurries or solutions of desired concentration levels.
Reference may be made to U.S. Pat. Nos. 1,806,287, 2,100,185, 2,310,265, 2,695,265, 2,772,372, 3,166,020, 3,186,769 and to Canadian Pat. No. 790,113 which disclose various eductor-mixer mixing systems, and air conveying apparatus in the same general field as the present invention.